A. J. Drexel Nanomaterials Institute and Department of Materials Science and Engineering , Drexel University , Philadelphia , Pennsylvania 19104 , United States.
Electrochemical Energy Systems Laboratory, Department of Mechanical Engineering and Mechanics , Drexel University , Philadelphia , Pennsylvania 19104 , United States.
ACS Nano. 2018 Mar 27;12(3):2685-2694. doi: 10.1021/acsnano.7b08889. Epub 2018 Feb 23.
Understanding the rheological properties of two-dimensional (2D) materials in suspension is critical for the development of various solution processing and manufacturing techniques. 2D carbides and nitrides (MXenes) constitute one of the largest families of 2D materials with >20 synthesized compositions and applications already ranging from energy storage to medicine to optoelectronics. However, in spite of a report on clay-like behavior, not much is known about their rheological response. In this study, rheological behavior of single- and multilayer TiCT in aqueous dispersions was investigated. Viscous and viscoelastic properties of MXene dispersions were studied over a variety of concentrations from colloidal dispersions to high loading slurries, showing that a multilayer MXene suspension with up to 70 wt % can exhibit flowability. Processing guidelines for the fabrication of MXene films, coatings, and fibers have been established based on the rheological properties. Surprisingly, high viscosity was observed at very low concentrations for solutions of single-layer MXene flakes. Single-layer colloidal solutions were found to exhibit partial elasticity even at the lowest tested concentrations (<0.20 mg/mL) due to the presence of strong surface charge and excellent hydrophilicity of MXene, making them amenable to fabrication at dilute concentrations. Overall, the findings of this study provide fundamental insights into the rheological response of this quickly growing 2D family of materials in aqueous environments as well as offer guidelines for processing of MXenes.
了解悬浮二维（2D）材料的流变性能对于各种溶液处理和制造技术的发展至关重要。2D 碳化物和氮化物（MXenes）构成了最大的二维材料家族之一，已有超过 20 种合成成分，应用范围从储能到医学到光电。然而，尽管有关于类粘土行为的报道，但人们对其流变响应知之甚少。在这项研究中，研究了单层和多层 TiCT 在水性分散体中的流变行为。研究了 MXene 分散体在各种浓度下的粘性和粘弹性特性，从胶体分散体到高负载浆料，结果表明高达 70wt%的多层 MXene 悬浮液可以表现出流动性。根据流变性能，制定了用于制造 MXene 薄膜、涂层和纤维的加工指南。令人惊讶的是，单层 MXene 薄片溶液在非常低的浓度下表现出高粘度。由于 MXene 表面电荷强和极好的亲水性，单层胶体溶液即使在最低测试浓度（<0.20mg/mL）下也表现出部分弹性，这使得它们能够在稀释浓度下进行制造。总的来说，这项研究的结果提供了对这种快速增长的二维材料家族在水相环境中的流变响应的基本了解，并为 MXenes 的加工提供了指导。
